Side project reminder

We all have side projects that we would like to do because they're cool or fun. However, in the stress of daily life, we quickly forget about it. What if there was an app that let you input interesting side projects that you want to do someday? You could tell the app how long it would take (1 hour, 1 day, etc.). Then the app would remind you to complete your project when you have free time. How does it know when you have free time? It could sync with your calendar and use that information.